drm/i915: Add helpers for BW management on shared display links

At the moment a modeset fails if the config computation of a pipe can't
fit its required BW to the available link BW even though the limitation
may be resolved by reducing the BW requirement of other pipes.

To improve the above this patch adds helper functions checking the
overall BW limits after all CRTC states have been computed. If the check
fails the maximum link bpp for a selected pipe will be reduced and all
the CRTC states will be recomputed until either the overall BW limit
check passes, or further bpp reduction is not possible (because all
pipes/encoders sharing the link BW reached their minimum link bpp).

Atm, the MST encoder allocates twice the required BW for YUV420 format
streams. A follow-up patchset will fix that, add a code comment about
this.

This change prepares for upcoming patches enabling the above BW
management on FDI and MST links.

v2:
- Rename intel_crtc_state::max_link_bpp to max_link_bpp_x16 and
  intel_link_bw_limits::max_bpp to max_bpp_x16. (Jani)
v3:
- Add the helper functions in a separate patch. (Ville)
- Add the functions to intel_link_bw.c instead of intel_atomic.c (Ville)
- Return -ENOSPC instead of -EINVAL to userspace in case of a link BW
  limit failure.
v4:
- Make intel_atomic_check_config() static.
v5: (Ville)
- Rename intel_link_bw_limits::min_bpp_pipes to min_bpp_reached_pipes
  and intel_link_bw_reset_pipe_limit_to_min() to
  intel_link_bw_set_min_bpp_for_pipe().
- Rename pipe_bpp to link_bpp in intel_link_bw_reduce_bpp().
- Add FIXME: comment about MST encoder's YUV420 BW allocation and
  tracking the link bpp limit accordingly.
v6:
- Move intel_link_bw_compute_pipe_bpp() to intel_fdi.c (Ville)
- WARN_ON(BIT(pipe) & min_bpp_reached_pipes) in
  intel_link_bw_set_bpp_limit_for_pipe(). (Ville)
- Rename intel_link_bw_set_min_bpp_for_pipe() to
  intel_link_bw_set_bpp_limit_for_pipe() and
  intel_link_bw_limits::min_bpp_reached_pipes to
  bpp_limit_reached_pipes. (Ville)
- Remove unused header includes.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921195159.2646027-10-imre.deak@intel.com

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